Here’s Why Waymo’s Robotaxis Freaked Out During The San Francisco Outage

• Waymo explains why its robotaxis froze this past weekend during a big power outage in San Francisco.
• The ride-hailing company temporarily suspended operations in the Bay Area.
• The power outage took down many traffic lights, and because of this, the autonomous cars sent a lot of confirmation requests to remote human operators.

Waymo, the biggest robotaxi operator in the United States, had a rough time in San Francisco this past weekend, when a huge power outage left approximately 130,000 residents without electricity.

The blackout also took out many traffic lights, and Waymo’s robotaxis were not happy about it. Several social media videos and photos showed the driverless Jaguar I-Pace EVs stuck at intersections, with their hazard lights on.

The company ultimately pulled the cars over temporarily and resumed operations after power had been restored to the majority of the affected area. But it caused some chaos, and now we know why. The Alphabet-owned driverless taxi firm issued an update, explaining what led to the frozen cabs.

In short, it all comes down to too many dark traffic lights, which led to a lot of confirmation requests sent back to home base, where human operators had to review each request and inform the vehicle what to do. The large number of calls back home created a backlog, which led to the driverless EVs freezing while waiting for an answer.

“While the Waymo Driver is designed to handle dark traffic signals as four-way stops, it may occasionally request a confirmation check to ensure it makes the safest choice,” the company wrote in a blog post. “While we successfully traversed more than 7,000 dark signals on Saturday, the outage created a concentrated spike in these requests. This created a backlog that, in some cases, led to response delays contributing to congestion on already-overwhelmed streets.”

I asked Waymo if slower-than-usual LTE upload and download speeds also played a role in the situation, and I’ll update this story when I hear back.

With this episode done and dusted, the Alphabet-owned robotaxi operator said it’s analyzing the event and is already making changes to the way the cabs handle situations like this. Waymo is now rolling out a fleet-wide update that gives its vehicles more context about regional outages. This should enable the EVs to navigate intersections with dark traffic lights more decisively, the company said.

“We established these confirmation protocols out of an abundance of caution during our early deployment, and we are now refining them to match our current scale,” the company said.